The invention relates to electrostatic precipitators and particularly to apparatus for cleaning the collection plates in such apparatus. The apparatus has particular application to precipitators having a capacity in the order of a few hundred cubic feet per minute up to about 6,000 cubic feet per minute. Apparatus of this nature is typically used in restaurants, bars, as well as industrial plants, machine shops, welding shops and the like. Much larger units having air flows of up to 1,000,000 cubic feet per minute are typically installed outdoors and are used in various industrial processes such as in the manufacturer of sulfuric acid. Known large electrostatic precipitators include eccentric cam shaft type mountings for hammers intended for cleaning of the collecting surfaces. Although such apparatus has been used in large electrostatic precipitators, such as those in process industries, such apparatus has not been readily adaptable to smaller installations typically used within commercial buildings.
The basic operating principle of the electrostatic precipitator is demonstrated by the familiar experiment in which a glass rod is rubbed with a slik cloth. The rod is thereby given an electrostatic charge, making it capable of attracting uncharged bits of paper, lint, or cork. In the electrostatic precipitator, the collecting surfaces are gounded, and a charge is created on the particles which are to be collected.
The power supply in such apparatus typically steps up line voltage and rectifies it to produce 5,000 to 15,000 volts of direct current. The direct current voltage is applied to a plurality of discharge electrode wires suspended in the gas flow path. The high potential on the discharge electrodes causes a corona discharge, from which electrons migrate out into the gas. These create gas ions, which attach themselves to particles in the gas and give the particles a charge.
Grounded collecting electrodes are also provided. The high potential difference results in a powerful electric field through which the gas is directed. In accordance with Coulomb's law, the field exerts a force on a charged particle in the field. This force moves particles out of the gas stream to the collecting electrodes. At the grounded collecting electrodes, the particles lose their charge.
The grounded collecting electrodes are typically plate shaped and are enclosed within a removable cell. When the precipitator is functioning properly, the collection plates will eventually become loaded with contaminant. In order to maintain efficiency the contaminants must be removed. The most common method of cleaning the cells, is to remove them from the unit and use a stream of liquid, an air blast, or simply a detergent wash. However, when the units are ceiling-hung (often 10 to 14 feet above the floor) the periodic removal of cells is an inconvenience, and automatic cleaning is desirable.
There are three methods currently used for automatic cleaning: A wash and drain system which requires piping hot water and detergent to each unit; a pneumatic vibrating system which also entails piping high pressure air to each cell which is in turn equipped with several pneumatic pistons; an electrical system which also employs vibrators attached to each cell. The latter system is relatively simple but is not very effective.
The water system is prone to nuisance leakage of the water that is sprayed on the plates. The other methods are only partially effective since a mere vibrating action removes only the outermost layer of the contaminant. Thus the precipitator still has reduced collection efficiency. Each of these methods collect the contaminants in a hopper installed below the cells.
It is an object of the invention to provide apparatus which is particularly suitable for remote installation, such as where the entire precipitator is mounted on the ceiling of a building.
It is another object of the invention to provide apparatus which will require a minimum of periodic maintenance.
It is still another object of the invention to provide apparatus which will be relatively inexpensive.